1. Field of the Invention
This invention relates to a control for an engine under a transitional condition and more particularly to an improved control device and method for a direct injected internal combustion engine under a transitional condition such as a quick acceleration.
2. Description of Related Art
In the interest of improving engine performance and particularly fuel efficiency and exhaust emission control, many types of engines now employ a fuel injection system for supplying fuel to the engine. In this system, generally fuel is injected into an air induction device. This fuel injection has the advantages of permitting the amount of fuel delivered for each cycle of the engine to be adjusted. In addition, by utilizing the fuel injection system, it is possible to maintain the desired fuel air ratio under a wide variety of engine running condition. In order to obtain still further improvements, a direct fuel injection system is being considered. This system injects fuel directly into the combustion chamber and thus has significant potential advantages rather than the indirect fuel injection noted above.
These features are particularly useful with two cycle engines, although not specifically limited thereto. Because the overlap between the scavenge port and exhaust port opening and closing give rise to the possibility that unburned hydrocarbons may pass into the atmosphere through the exhaust port. In addition, amounts of exhaust gases remaining in the combustion chamber relatively under light speeds and loads can cause misfiring and eventually unburned hydrocarbons again pass through the atmosphere.
In operation, a control device for the injection systems increases the amount of fuel that is supplied to the fuel injector under the transitional conditions, that the engine load is increasing. Such transitional conditions include an acceleration of the engine speed. The larger the rate of the increase of the load is, the larger amount of fuel the engine requires. This situation is, for example, a quick acceleration of the engine speed.
Meanwhile, the injected fuel needs certain time for diffusion. If the fuel is injected in the air induction device, it has enough time for diffusion before entering into the combustion chamber. However, in the direct cylinder injection, the fuel has relatively meager time for diffusion and this can result in incomplete combustion. This incomplete combustion is likely to give the operator uneasy feeling such as a slow rate of acceleration.
The problem is prominent, for instance, in two stroke engines wherein an ignition timing comes almost immediately after the end of the injection timing. Even in four stroke engines under a full or almost full speed operation as is typical in marine engines such as outboard motors that are usually operated under high load conditions, ignition occurs shortly after the completion of injection. This is because this running condition requires a relatively long duration of injection. In short, these engines under such conditions may fire the fuel air charge before completion of the fuel diffusion and hence can invite the aforenoted problem.
In addition, the two cycle engine operates on a crankcase compression principle. Air charge is induced into the crankcase chamber first and then transferred to the combustion chamber through scavenge passages. Because of this, in the transitional period, there is a large discrepancy between the engine requirement and an actual amount of the induced air.
Usually, under a quick acceleration condition, an amount of the air charge entering into the combustion chamber from the crankcase chamber in the transitional period will not be consistent with a required amount until one or two combustion cycles elapse. In other words, an actual air charge amount deviates from a required amount during these one or two combustion cycles.
This state is shown in FIG. 1 that illustrates an interrelationship between the number of combustion cycles and the amount of induced air charge per combustion cycle. As seen in this figure, the actual amount of the induction air charge that is Q2 at the first instance of the transitional period Tr reaches the amount of the engine requirement Q1 and only becomes stable at the third combustion cycle. The deviation results in an incorrect fuel air ratio and eventually difficulties in control of emissions discharged from the exhaust ports. It should be noted that the transitional period Tr in FIG. 1 does not coincide with the transitional condition such as an acceleration condition. The transitional condition is longer than the transitional period. The relationship shown in FIG. 1 will be described more in detail with the description of the control routine shown in FIG. 6.
It is, therefore, a principal object of this invention to provide a direct injection control system that can improve combustion states under the transitional conditions in which the engine load is increasing not to give the operator uneasy feeling and also to remove difficulty in control of emissions.
This invention is adapted to be embodied in a direct cylinder, internal combustion engine.
In accordance with one aspect of this invention, the engine has an engine body that defines at least one cylinder bore in which a piston reciprocates to rotate a crankshaft. A cylinder head is affixed to one end of the engine body for closing the cylinder bore and defining with the piston and the cylinder bore a combustion chamber. An air induction device that has a throttle valve is provided for admitting an air charge to the combustion chamber. A fuel injector is provided for spraying fuel directly into the combustion chamber for combustion therein. Means for sensing rotational speeds of the crankshaft is provided. Means for sensing openings of the throttle valve is provided. A control device is provided for increasing the fuel amount in response to the output from the throttle valve openings sensing means when the output becomes larger than before. The control device further reduces the increase amount of the fuel when the output from the crankshaft rotational speeds sensing means is within a predetermined range and the output from the throttle valve openings sensing means is larger than a predetermined value.
In accordance with another aspect of this invention, the engine has an engine body that defines at least one cylinder bore in which a piston reciprocates. A cylinder head is affixed to one end of the engine body for closing the cylinder bore and defining with the piston and the cylinder bore a combustion chamber. An air induction device is provided for admitting an air charge to the combustion chamber. A fuel injector is provided for spraying fuel directly into the combustion chamber for combustion therein. Means for sensing amounts of the air charge is provided. Means for controlling amounts of the fuel is provided. The fuel amounts control means primarily increases the fuel amount in response to the output from the air charge amounts sensing means when the air charge amount required by said engine is increasing. The fuel amounts control means further reduces the increase amount of the fuel in response to the output from the air charge amounts sensing means when the difference between the air charge amount required by the engine and the actual air charge amount is larger than a predetermined value.
In accordance with a method for practicing this invention with the engine that comprises an engine body defining at least one cylinder bore in which a piston reciprocates to rotate a crankshaft, a cylinder head affixed to one end of said engine body for closing the cylinder bore and defining with the piston and the cylinder bore a combustion chamber, an air induction device having a throttle valve for admitting an air charge to the combustion chamber, a fuel injector for spraying fuel directly into the combustion chamber for combustion therein, the method has the step of sensing the opening of the throttle valve. A step of increasing the fuel amount is provided when the opening is larger than before. A step of sensing the rotational speed of the crankshaft and reducing the increase amount of the fuel is provided when the rotational speed is within a predetermined range and the opening is larger than a predetermined value.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.